Flexible Use of an Inverter in a Refrigeration Unit

ABSTRACT

A control system for a refrigeration unit being powered by a power source and having a compressor, an inverter and an evaporator fan is provided. The control system may include a first switch configured to selectively couple the compressor with one of the power source and the inverter, a second switch configured to selectively couple the evaporator fan with one of the power source and the inverter, and a controller operatively coupled to the first and second switches. The controller may be configured to engage the first and second switches into one of a first state and a second state based on a triggering event. In the first state, the first switch may be configured to couple the compressor with the power source and the second switch may be configured to couple the evaporator fan with the inverter. In the second state, the first switch may be configured to couple the compressor with the inverter and the second switch may be configured to couple the evaporator fan with the power source.

FIELD OF THE DISCLOSURE

The present disclosure generally relates to refrigeration units, andmore particularly, to systems and methods for controlling arefrigeration unit using a flexible inverter configuration.

BACKGROUND OF THE DISCLOSURE

Refrigeration systems are generally used to maintain a relatively lowtemperature within a designated area. Refrigeration systems serve toremove heat from a substantially enclosed area and transfer the heat toan environment external to the enclosed area. Refrigeration systems arecommonly used in association with residential and commercial foodrefrigerators, air-conditioning units in homes and automobiles, as wellas with refrigerated cargos of ships and trucks. Mobile refrigerationsystems used to condition frozen and perishable loads in cargo spaces oftrucks and trailers are referred to as transport refrigeration units.

The basic components of a refrigeration unit for residential, commercialor mobile applications typically include a compressor, condenser coil,condenser fan, expansion valve, evaporator coil and evaporator fan.Residential refrigerators typically employ single-speed compressors thatare either in an on or an off state and can only operate at one speed.Such refrigeration systems are unable to effectively adapt to thevarying conditions that occur throughout the day, and further, areunable to efficiently use electric power once the unit is at a steadystate.

Efforts have been made to improve energy consumption and performance ina refrigeration unit by employing an inverter compressor. In a typicalinverter compressor configuration, an inverter is used to supply pulsedpower to a compressor in a controlled manner. The inverter compressor iscapable of operating at a number of desired speeds, depending on thedesired application and the degree of cooling required of therefrigeration unit. While such variable control of the compressorenables quicker cooling capabilities and less power consumption atsteady state by operating the compressor at lower speeds, there is stillmuch room for improvement.

Refrigeration units are typically configured to cool at a specific rateat full load. This often results in the combination of an inverter witha relatively high load capacity and a compressor with a relatively lowload capacity, as depicted in FIG. 1. The compressor is driven to ahigher speed for full load operation (pull down or start/stop) and at alower speed by the inverter for other load demands. Accordingly, theactual load on the refrigeration unit is not at full load capacity atall times. In fact, the load experienced by the refrigeration unitduring most of its operations is actually much less. Such a combinationof a high load capacity inverter with a low load capacity compressorresults in efficiency loss and decreased capacity modulation.Furthermore, the cooling demand from the internal fan associated withthe inverter increases during full load operation, resulting in greaterpower consumption. In addition, if the inverter also provides power tothe evaporating fan, the air flow provided by the evaporator fan willoften be insufficient for use with steady state operations.

The disclosed systems and methods are directed at overcoming one or moreof the deficiencies set forth above.

SUMMARY OF THE DISCLOSURE

In accordance with one aspect of the disclosure, a control system for arefrigeration unit being powered by a power source and having acompressor, an inverter and an evaporator fan is provided. The controlsystem may include a first switch configured to selectively couple thecompressor with one of the power source and the inverter, and a secondswitch configured to selectively couple the evaporator fan with one ofthe power source and the inverter. The control system may additionallyinclude a controller operatively coupled to the first and secondswitches and configured to engage the first and second switches into oneof a first state and a second state based on a triggering event. In thefirst state, the first switch may be configured to couple the compressorwith the power source and the second switch may be configured to couplethe evaporator fan with the inverter. In the second state, the firstswitch may be configured to couple the compressor with the inverter andthe second switch may be configured to couple the evaporator fan withthe power source.

In accordance with another aspect of the disclosure, a control systemfor a refrigeration unit being powered by a power source and having acompressor and an evaporator fan is provided. The control system mayinclude an inverter in communication with the power source, and one ormore switches configured to selectively supply power from one of thepower source and the inverter to the compressor and the evaporator fan.The control system may further include a controller operatively coupledto the switches and configured to engage the switches into one of afirst state and a second state based on a triggering event. In the firststate, the controller may engage the switches to couple the power sourcewith the compressor and the inverter with the evaporator fan. In thesecond state, the controller may engage the switches to couple theinverter with the compressor and the power source with the evaporatorfan.

In accordance with yet another aspect of the disclosure, a method forcontrolling a refrigeration unit being powered by a main power sourceand having a compressor, an inverter and an evaporator fan is provided.The method may determine a load demand of the refrigeration unit,generate a triggering event in response to a substantial change in theload demand, and simultaneously interchange the power supplied to eachof the compressor and the evaporator fan in response to the triggeringevent.

Other advantages and features will be apparent from the followingdetailed description when read in conjunction with the attacheddrawings.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a diagrammatic view of a prior art embodiment of arefrigeration unit;

FIG. 2 is a schematic view of the prior art embodiment of FIG. 1;

FIG. 3 is a diagrammatic view of one exemplary refrigeration controlsystem; and

FIG. 4 is a graphical view of a temperature profile associated with theexemplary refrigeration control system of FIG. 3.

It should be understood that the drawings are not necessarily to scaleand that the disclosed embodiments are sometimes illustrateddiagrammatically and in partial views. In certain instances, detailswhich are not necessary for an understanding of the disclosed methodsand systems or which render other details difficult to perceive may havebeen omitted. It should be understood, of course, that this disclosureis not limited to the particular embodiments illustrated herein.

DETAILED DESCRIPTION OF THE DISCLOSURE

Referring to FIG. 2, a schematic diagram of a conventional refrigerationunit 100 is provided. The refrigeration unit 100 may include acompressor 102, a condenser coil 104, a condenser fan 106 with acondenser motor 108, an expansion valve 110, an evaporator coil 112, anevaporator fan 114 with an evaporator motor 116, and refrigerant 118.The refrigerant may include, for example, fluorinated carbons,chlorinated carbons, brominated carbons, carbon dioxide, ammonia,ethane-based refrigerants, methane-based refrigerants, water, or anyother refrigerant commonly used in the art for the purposes of absorbingand transferring heat. Refrigerants may absorb heat by evaporating andchanging its state from a liquid to a gas, for example, at lowtemperatures and pressures, and release heat by condensing and changingits state from a gas back to a liquid, for example, at highertemperatures and pressures.

As shown in FIG. 2, the refrigerant 118 may enter the compressor 102 ina high-temperature, low-pressure gas state. The compressor 102 maycompress the refrigerant 118 into a high-temperature, high-pressure gasstate. In this state, the refrigerant 118 may flow through the condensercoil 104 and liquefy while releasing heat. The heat emitted by therefrigerant 118 may be absorbed by the condenser coil 104. The condenserfan 106 may then circulate cool air across the condenser coil 104 so asto transfer the heat from the condenser coil 104 to an exteriorenvironment. The expansion valve 110 may then reduce the pressure of therefrigerant 118 as the refrigerant 118 flows through the expansion valve110, creating a low-temperature, low-pressure liquid. Thelow-temperature, low-pressure liquid refrigerant 118 may flow throughthe evaporator coil 112 while the evaporator fan 114 draws heat from adesired area to be cooled, for example, a refrigeration cabinet 120, andcirculates the heat across the evaporator coil 112. The heat may then beabsorbed and drawn away by the refrigerant 118 as it flows through theevaporator coil 112. As the refrigerant 118 absorbs the heat, therefrigerant 118 may change from liquid back to gas.

In order for the refrigerant 118 to absorb and transfer the maximumamount of heat, the basic components in the refrigerant unit 100, forexample, the compressor 102 and evaporator fan 114 of FIG. 2, may needto operate efficiently. The compressor 102 may generally serve as a pumpto control the circulation of the refrigerant 118, and it may addpressure to the refrigerant 118 so as to increase its temperature. Theevaporator fan 114 may serve to circulate the air flow, particularly inthe cabinet 120. Among other things, inefficient operation of thecompressor 102 and/or the evaporator fan 114 may result in unevendistribution of temperature within the cabinet 120 as well as inaccuratetemperature readings. Accordingly, it is a shared interest to providemeans for controlling the compressor 102 and the evaporator fan 114 ofthe refrigeration unit 100 as efficiently as possible.

Turning now to FIG. 3, one exemplary embodiment of a refrigerationcontrol system 200 with a flexible inverter configuration is provided.In the particular embodiment shown, the compressor 202 and theevaporator fan 214 may be arranged so as to receive power from aninverter 204 and a main power source 206. The compressor 202 mayinclude, for example, a rotary screw compressor, a reciprocatingcompressor, a scroll compressor, a centrifugal compressor, or the like.The main power source 206 may include a direct current (DC) powersource, an alternating current (AC) power source, or any other powersource suitable for use with the refrigeration control system 200.Furthermore, the inverter 204 may be configured to receive powersupplied by the main power source 206, and output a pulsed power signalof a predetermined frequency to one of the compressor 202 and theevaporator fan 214.

Still referring to FIG. 3, the control system 200 may include one ormore switches 208, 210 that are configured to selectively supply powerfrom one of the inverter 204 and the main power source 206 to thecompressor 202 and the evaporator fan 214. In one embodiment, thecontrol system 200 may include a first switch 208 that is associatedwith the compressor 202 and a second switch 210 that is associated withthe evaporator fan 214. Moreover, the first switch 208 may be configuredto selectively couple the compressor 202 with one of the inverter 204and the main power source 206, while the second switch 210 may similarlybe configured to selectively couple the evaporator fan 214 with one ofthe inverter 204 and the main power source 206. Each of the first andsecond switches 208, 210 may be switchable between a first state 208 a,210 a and a second state 208 b, 210 b. For example, in the first state208 a, 210 a, the first switch 208 may cause the compressor 202 to be inelectrical communication with the main power source 206, while thesecond switch 210 may cause the evaporator fan 214 to be in electricalcommunication with the inverter 204. Correspondingly, in the secondstate 208 b, 210 b, the first switch 208 may cause the compressor 202 tobe in electrical communication with the inverter 204, while the secondswitch 210 may cause the evaporator fan 214 to be in electricalcommunication with the main power source 206. The switches 208, 210 ofFIG. 3 may include latches, relays, analog switches, digital switches,or any other controllable switch commonly used in the art. Furthermore,each of the switches 208, 210 may be configured to engage simultaneouslyor after a predetermined delay with respect to one another. Inalternative embodiments, the control system 200 may employ a singleswitch or an array of switches configured to interface each of thecompressor 202 and the evaporator fan 214 with the appropriate powersource.

As shown in FIG. 3, a controller 216 may be provided to control each ofthe first and second switches 208, 210 and engage the switches 208, 210in response to significant changes in the operating conditions of therefrigeration control system 200. In one exemplary embodiment, thecontroller 216 may be configured to generate a triggering event inresponse to the detection of any uneven distribution of temperaturewithin the associated cabinet 120. To compensate for uneven temperaturedistribution, for example, the controller 216 may be configured toengage each of the first and second switches 208, 210 into the secondstate 208 b, 210 b so as to couple the compressor 202 with the inverter204 and to couple the evaporator fan 214 to the main power source 206.More specifically, by providing direct power from the main power source206 to the evaporator fan 214, the evaporator fan 214 may be able tooperate at full potential so as to more effectively circulate and evenlydistribute the air within the cabinet 120. Furthermore, by providingpulsed power from the inverter 204 to the compressor 202, operation ofthe compressor 202 may be maintained more efficiently. The controller216 may hold the switches 208, 210 in the second state 208 b, 210 buntil temperatures within the cabinet 120 exhibit even distribution, atwhich point the controller 216 may restore each of the first and secondswitches 208, 210 to the first state 208 a, 210 a.

In alternative embodiments, the controller 216 of FIG. 3 may beconfigured to generate a triggering event in response to the amount ofcooling that is required, or the load demand. For example, during fullload operation or when maximum cooling is required, the controller 216may engage the first and second switches 208, 210 into the first state208 a, 210 a. Accordingly, in response to relatively high load demands,the compressor 202 may be powered by the main power source 206 to beoperated at a higher capacity, while the less essential evaporator fan214 may be supplied with pulsed power from the inverter 204. Thecontroller 216 may hold the switches 208, 210 in the first state 208 a,210 a until air within the cabinet 120 reaches a desired temperature, oruntil a steady state has been reached. At steady state, the load demandmay be lowered as temperatures within the cabinet 120 only need to bepreserved and not lowered. Thus, in response to a relatively low loaddemand, or at part load, the controller 216 may be configured to engageeach of the first and second switches 208, 210 into the second state 208b, 210 b. Moreover, at part load, the evaporator fan 214 may be poweredby the main power source 206 so as to operate at higher capacity andprovide proper circulation of air within the cabinet 120. As lesscooling is required, the compressor 202 may in turn be supplied withpulsed power from the inverter 204. In further modifications, therefrigeration control system 200 may be configured to simultaneouslyoperate both of the compressor 202 and the evaporator fan 214 at eitherhigh capacity or low capacity depending on the immediate load demand.Specifically, the controller 216 and the switches 208, 210 may beconfigured to couple both of the compressor 202 and the evaporator fan214 to either the main power source 206 or the inverter 204. In stillfurther alternatives, the controller 216 and the switches 208, 210 maybe configured to disconnect power to both of the compressor 202 and theevaporator fan 214 during certain steady state conditions.

With reference to the graph of FIG. 4, a temperature profile of acabinet 120 being cooled by the exemplary refrigeration control system200 is provided. As shown, during full load operations, the initialtemperature within the cabinet 120 may be exponentially decreased untilthe temperature reaches a desired set point or steady state. Suchcharacteristics may be responsive to operating the compressor 202 at arelatively high capacity with the main power source 206 as well assimultaneously operating the evaporator fan 214 at a relatively lowcapacity with the inverter 204, as in the control system 200 of FIG. 3for example. During part load operations, or once the desired set pointhas been reached, the temperature within the cabinet 120 may effectivelybe maintained within an acceptable range of the set point using minimalpower. Such characteristics may be responsive to operating thecompressor 202 at a relatively low capacity with the inverter 204 whilesimultaneously operating the evaporator fan 214 at a relatively highcapacity with the main power source 206 to maintain proper circulation.

Accordingly, the controller 216 of FIG. 3, for instance, may beconfigured to initially determine and to continuously monitor a loaddemand of the refrigeration control system 200. If the controller 216determines a substantial change in the load demand, the controller 216may then proceed to generate a triggering event in response to thechange. Furthermore, in response to the triggering event, the controller216 may be configured to simultaneously interchange the power suppliedto each of the compressor 202 and the evaporator fan 214 based on thetype of triggering event generated. If the triggering event indicates asubstantial increase in load demand, the controller 216 of FIG. 3, forexample, may engage the switches 208, 210 into the first state 208 a,210 a until an additional triggering event is generated.Correspondingly, if the triggering event indicates a substantialdecrease in load demand, or once the desired set point has been reached,the controller 216 of FIG. 3 may engage the switches 208, 210 into thesecond state 208 b, 210 b until the refrigeration control system 200 ispowered off or until the load demand increases again.

Such implementations of a flexible inverter configuration as disclosedherein may desirably enable the use of a compressor with a relativelyhigher load capacity and an inverter with a relatively lower loadcapacity, as compared with the embodiments of the prior art. Inparticular, the use of a higher capacity compressor during full loadoperations may result in minimized power consumption and optimizedperformance when it is being powered directly by the main power source206. Moreover, the use of a higher capacity compressor during part loadoperations may result in lower and more controlled speeds when it isbeing powered by the inverter 204. Furthermore, as the inverter is notrequired to operate the compressor during all modes of operation, forexample, during full load operations, a lower capacity inverter as wellas a lower capacity inverter fan may be employed. More specifically, theload capacity of the compressor may be at least 1.5 times greater thanthe load capacity of the inverter.

While only certain embodiments have been set forth, alternatives andmodifications will be apparent from the above description to thoseskilled in the art. These and other alternatives are consideredequivalents and within the spirit and scope of this disclosure and theappended claims.

What is claimed is:
 1. A control system for a refrigeration unit beingpowered by a power source and having a compressor, an inverter and anevaporator fan, the control system comprising: a first switch configuredto selectively couple the compressor with one of the power source andthe inverter; a second switch configured to selectively couple theevaporator fan with one of the power source and the inverter; and acontroller operatively coupled to the first and second switches andconfigured to engage the first and second switches into one of a firststate and a second state based on a triggering event, the first switchbeing configured to couple the compressor with the power source and thesecond switch being configured to couple the evaporator fan with theinverter in the first state, the first switch being configured to couplethe compressor with the inverter and the second switch being configuredto couple the evaporator fan with the power source in the second state.2. The control system of claim 1, wherein the first state corresponds tofull load operation of the refrigeration unit and the second statecorresponds to part load operation of the refrigeration unit.
 3. Thecontrol system of claim 1, wherein the triggering event corresponds to achange in load demand of the refrigeration unit, the controller beingconfigured to engage the first and second switches into the first stateduring full load operation and into the second state during part loadoperation.
 4. The control system of claim 1, wherein the triggeringevent corresponds to a change in temperature distribution within acabinet of the refrigeration unit.
 5. The control system of claim 1,wherein the controller is configured to engage the first and secondswitches into the second state in response to any uneven temperaturedistribution detected within the cabinet.
 6. The control system of claim1, wherein the controller is configured to engage the first and secondswitches into the first state in response to even temperaturedistribution within the cabinet.
 7. The control system of claim 1,wherein the compressor has a relatively higher load capacity than thatof the inverter.
 8. The control system of claim 7, wherein the loadcapacity of the compressor is greater than that of the inverter by atleast 1.5 times.
 9. A control system for a refrigeration unit beingpowered by a power source and having a compressor and an evaporator fan,the control system comprising: an inverter in communication with thepower source; one or more switches configured to selectively supplypower from one of the power source and the inverter to the compressorand the evaporator fan; and a controller operatively coupled to theswitches and configured to engage the switches into one of a first stateand a second state based on a triggering event, the controller engagingthe switches to couple the power source with the compressor and theinverter with the evaporator fan in the first state, the controllerengaging the switches to couple the inverter with the compressor and thepower source with the evaporator fan in the second state.
 10. Thecontrol system of claim 9, wherein the first state corresponds to fullload operation of the refrigeration unit and the second statecorresponds to part load operation of the refrigeration unit.
 11. Thecontrol system of claim 9, wherein the triggering event corresponds to achange in load demand of the refrigeration unit, the controller beingconfigured to engage the switches into the first state during full loadoperation and into the second state during part load operation.
 12. Thecontrol system of claim 9, wherein the triggering event corresponds to achange in temperature distribution within a cabinet of the refrigerationunit.
 13. The control system of claim 9, wherein the controller isconfigured to engage the switches into the second state in response toany uneven temperature distribution detected within the cabinet.
 14. Thecontrol system of claim 9, wherein the controller is configured toengage the first and second switches into the first state in response toeven temperature distribution within the cabinet.
 15. The control systemof claim 9, wherein a load capacity of the inverter is substantiallyless than that of the compressor.
 16. The control system of claim 9,wherein the switches include at least a first switch corresponding tothe compressor and a second switch corresponding to the evaporator fan,the controller being configured to engage the switches between the firstand second states simultaneously.
 17. The control system of claim 9,wherein the inverter is configured to supply pulsed power to one of thecompressor and the evaporator fan.
 18. A method for controlling arefrigeration unit being powered by a main power source and having acompressor, an inverter and an evaporator fan, comprising the steps of:determining a load demand of the refrigeration unit; generating atriggering event in response to a substantial change in the load demand;and simultaneously interchanging the power supplied to each of thecompressor and the evaporator fan in response to the triggering event.19. The method of claim 18, wherein the triggering event is generatedwhen the load demand of the refrigeration unit changes from full to partload or from part to full load.
 20. The method of claim 18, wherein thecompressor is powered by the main power source and the evaporator fan ispowered by the inverter during full load operation, and the compressoris powered by the inverter and the evaporator fan is powered by the mainpower source during part load operation.